There are at least three important elements involved in the formation of pavement constructions which carry vehicular traffic. Those elements include (a) the subgrade or supporting soil which can comprise a natural deposit or man-made fill, (b) a base course located above the subgrade which transmits the pressures exerted by the vehicle to the subgrade, and (c) a surface course, located above the base course, which is in direct contact with the vehicle.
The operation of the base course in a concrete pavement is not particularly critical since the concrete is quite rigid, and, therefore, shearing stresses in the base course are minimal. In the case of flexible pavement, however, the base course functions to transmit relatively high stresses to the subgrade. Thus, the nature of the base course is critical if a flexible pavement construction is used.
Some current construction practices involve the use of crushed stone or other granular materials for base courses. These aggregates, however, exhibit a lack of cohesion, are subject to densification under traffic conditions, and have relatively low shearing strengths under concentrated loads. A significant development in the prior art involves the use of a mixture of lime, an aggregate (such as crushed stone, gravel-containing soil or slag), and fly ash--these mixtures have been satisfactory from most standpoints. However, materials employed in these compositions are expensive either due to their scarcity or to the production and handling costs.
It is an object of this invention to utilize the material produced from the incineration of municipal waste as a component of a base course construction, and to avoid the need to dispose of that material in landfill sites.
It is another object of this invention to provide an improved material for pavement construction that is economical to produce and which can be employed in an efficient fashion.
It is an additional object of this invention to provide a material which is particularly suitable for use as the base course located beneath flexible pavement constructions for the reason that the material possesses the requisite strength for distributing loads on the pavement.
It is a further object of this invention to provide a material for use as a base course in flexible pavement constructions which is economical to produce, which comprises a minimum of relatively inexpensive ingredients and which can be handled and utilized in a highly efficient manner.
These and other objects of this invention will appear hereinafter, and it will be understood that the following examples are provided for purposes of illustration and not by way of limitation.